The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Torque model data is often gathered on a dynamometer with all cylinders of an engine being fueled. However, some engines now use partial cylinder deactivation to reduce pumping losses and increase fuel economy. For example, four cylinders out of an eight cylinder engine may be deactivated to reduce pumping losses. In addition, some engines may deactivate all cylinders of the engine during deceleration, which reduces fuel usage. In addition, the pumping losses and rubbing friction of the engine with all cylinders deactivated may create a negative torque (braking torque) that helps to slow the vehicle. To accommodate these types of engines, adjustments may be made for torque estimation and control to account for the number of cylinders that are actually being fueled.
The torque produced by the activated (fueled) cylinders may be referred to as indicated torque or cylinder torque. Flywheel torque may be determined by subtracting rubbing friction, pumping losses, and accessory loads from the indicated torque. Therefore, in one approach to estimating torque with partial cylinder deactivation, the indicated torque is multiplied by a fraction of cylinders being fueled to determine a fractional indicated torque. The fraction is the number of cylinders being fueled divided by the total number of cylinders. Rubbing friction, pumping losses, and accessory loads can be subtracted from the fractional indicated torque to estimate an average torque at the flywheel (brake torque) for partial cylinder deactivation.